Catalysis Of Water Gas Shift Reaction Research Articles

Process modelling for the production of hydrogen-rich gas from gasification of coal using oxygen, CO2 and steam reactants

This process modelling studied the effect of different reactants on syngas composition and gasifier heat duty (heat energy required to carry out the operation) and the downstream treatment of CO rich syngas to maximise hydrogen yield. The process modelling was validated against experimental data obtained from a large bench-scale entrained flow gasifier. Results show that considering the H2/CO ratio, the steam-O2 reactant favours the most compared to those of the pure oxygen and oxygen-CO2 reactants. Under comparable operating conditions, the highest H2/CO ratio of 0.74 was determined using steam-O2 reactant compared to that of 0.31 and 0.33 using steam-CO2 and pure oxygen reactant. The catalytic water-gas shift reaction (WGSR) favours the yield of H2 with complete CO conversion at a temperature of 400 °C using the steam/coal ratio of 1.2. Supplying steam in the gasifier requires more heat energy to be supplied to drive endothermic gasification reaction and maintain the gasifier temperature. Under complete carbon conversion, steam-CO2 and steam-oxygen reactants require 5–65 kW more energy than pure oxygen.

High-Efficiency Water Gas Shift Reaction Catalysis on α-MoC Promoted by Single-Atom Ir Species

Single-atom catalysts (SACs) with complete dispersion of metal species on substrates provide the ultimate atom economy and opportunities for improved heterogenous catalysis or to develop more catal...

Ultra-low temperature water–gas shift reaction catalyzed by homogeneous Ru-complexes in a membrane reactor – membrane development and proof of concept

Supported ionic liquid-phase (SILP) catalyzed water–gas shift reaction with in situ product removal is presented. A facilitated transport membrane coated onto the smooth outside of the SiC monolith allowed preferential removal of CO2 compared to H2.

Fabrication of oxygen vacancies through assembling an amorphous titanate overlayer on titanium oxide for a catalytic water–gas shift reaction

Superior catalytic performance in a water–gas shift reaction is achieved by fabricating oxygen vacancies through assembling a titanate overlayer on a TiO2 surface.

Efficient Waste to Energy Conversion Based on Co-CeO2 Catalyzed Water-Gas Shift Reaction

Waste to energy technology is attracting attention to overcome the upcoming environmental and energy issues. One of the key-steps is the water-gas shift (WGS) reaction, which can convert the waste-derived synthesis gas (H2 and CO) to pure hydrogen. Co–CeO2 catalysts were synthesized by the different methods to derive the optimal synthetic method and to investigate the effect of the preparation method on the physicochemical characteristics of Co–CeO2 catalysts in the high-temperature water-gas shift (HTS) reaction. The Co–CeO2 catalyst synthesized by the sol-gel method featured a strong metal to support interaction and the largest number of oxygen vacancies compared to other catalysts, which affects the catalytic activity. As a result, the Co–CeO2 catalyst synthesized by the sol-gel method exhibited the highest WGS activity among the prepared catalysts, even in severe conditions (high CO concentration: ~38% in dry basis and high gas hourly space velocity: 143,000 h−1).

O-exchange evidenced in Ce-Ni-MFI catalysts during water gas shift reaction: Use of isotopic water (50% H218O - 50% H216O)

This study provides a detailed O-exchange of Ce-MFI, Ni-MFI and Ce-Ni-MFI using isotopic water (50% H218O - 50% H216O) to better understand the reaction mechanism of the catalytic water gas shift reaction (WGSR) over different combinations of Ni and Ce incorporated in the MFI structure. The study showed high activity of incorporated Ce on water splitting, and explained how adding Ce to Ce-Ni-MFI as a catalyst in the WGSR increased its performance and selectivity. A detailed kinetic study was performed at low temperatures (503–533 K) on Ce-Ni-MFI (with 2 wt% Ni and 2 wt% Ce) using empirical, microkinetic and neural networks techniques. All these methods predicted the reaction rate very well. The suggested reaction mechanism from the microkinetic approach was consistent with the findings of the O-exchange study, and showed the cooperation of Ni and Ce to provide the required oxygen to oxidize CO on the Ni surface.

Mechanism of the Water-Gas Shift Reaction Catalyzed by Efficient Ruthenium-Based Catalysts: A Computational and Experimental Study.

Supported ionic liquid phase (SILP) catalysis enables a highly efficient, Ru-based, homogeneously catalyzed water-gas shift reaction (WGSR) between 100 °C and 150 °C. The active Ru-complexes have been found to exist in imidazolium chloride melts under operating conditions in a dynamic equilibrium, which is dominated by the [Ru(CO)3 Cl3 ]- complex. Herein we present state-of-the-art theoretical calculations to elucidate the reaction mechanism in more detail. We show that the mechanism includes the intermediate formation and degradation of hydrogen chloride, which effectively reduces the high barrier for the formation of the requisite dihydrogen complex. The hypothesis that the rate-limiting step involves water is supported by using D2 O in continuous catalytic WGSR experiments. The resulting mechanism constitutes a highly competitive alternative to earlier reported generic routes involving nucleophilic addition of hydroxide in the gas phase and in solution.

Synergetic effects of cerium and nickel in Ce-Ni-MFI catalysts on low-temperature water-gas shift reaction

Synergistic effects between nickel and cerium in catalytic water gas shift reaction (WGSR) have been widely reported, mostly using cerium as an active support coupled with nickel as a dispersed phase. Although, these metals are extensively used in industry, and their price has continuously raised, catalysts containing highly dispersed nickel and cerium are less investigated. This work tackles catalysts with low percentages (0–3 wt%) of well dispersed nickel and cerium in MFI framework. Catalysts containing only incorporated cerium exhibited no activity, while the single metal Ni-MFI series catalyzed the reaction. The prepared Ni-Ce-MFI series synergistically accelerated WGSR even at temperatures as low as 503 K, and some reach equilibrium conversion below 548 K. The catalytic performance increased by nickel content, and catalysts with similar mass percentage of cerium and nickel outperformed others. Furthermore, their maximum reduction temperatures occurred at ∼60 K lower, confirming their higher performance in WGSR.

Development and characterization of novel combinations of Ce‐Ni‐MFI solids for water gas shift reaction

AbstractIn this work, novel catalysts with different low percentages of nickel and cerium (0–3 % g/g) inside a crystalline silica framework were prepared to be tested in catalytic water gas shift reaction (WGSR) at low temperatures. The developed preparation method is distinctive as it does not require the impregnation of metals, drying, and further calcinations steps, and produces the anticipated catalysts in an efficient way. The produced solids were characterized using various characterization methods including XRD, TPR‐TPO, TPD, SEM/EDX, and N2 physisorption. Results indicated that these solids benefit from good reproducibility and ease of mass production. WGSR experiments over the produced solids at 503 K showed that Ce‐MFI solids were inactive at this temperature; however, Ni‐MFI and Ce‐Ni‐MFI solids catalyzed the reaction. At this low temperature, the catalysts containing cerium presented higher activity compared to catalysts with only nickel content. Furthermore, no methane production was observed using these catalysts.

DFT study of the enhancement on hydrogen production by alkaline catalyzed water gas shift reaction in supercritical water

Supercritical water gasification (SCWG) is hopefully to be an acceptable choice for hydrogen production, the hydroxide ion assisted water gas shift reaction (WGSR) has been regarded as the most important reaction to generate hydrogen during the process. However, the principle of practical OH− catalyzed reaction is not possible to acquire by experiments. Thus, density functional theory (DFT) is utilized to investigate the reaction mechanism theoretically in this work. Through first principle calculations, every species and energy barrier for elementary steps are achieved, and formate ion is determined as the important intermediate. Besides, HCOO− + H2O → HCO3− + H2 is the dominant path to generate hydrogen, as well as the rate-determining step with 47.94 kcal/mol energy barrier. Furthermore, the reaction rate constant is calculated to be kcatalytic(s−1) = 2.34 × 1012exp(−1.80 × 105/RT) using transition state theory with Wigner transmission coefficient (TST/w). Lastly, supercritical water condition is demonstrated to be a favored media for WGSR, because it may dissociate, dissolve or hydrolyze more hydroxide anion than conventional steam. The results are expected to benefit the control of reaction process and the design of SCWG reactor.

Mechanisms of the Water–Gas Shift Reaction Catalyzed by Carbonyl Complexes Mo(CO)6 and Mo2(CO)10: A Density Functional Theory Study

Four different mechanistic pathways for Mo(CO)6 and a reaction mechanism for the binuclear species Mo2(CO)10 catalyzed water–gas shift reaction (WGSR) have been analyzed using density functional method. It turned out that the binuclear catalyst provides more facile transformations through lower barriers in comparison to the mononuclear catalyst, which is explained by the metal–metal cooperativity between the two Mo centers. The energy span model indicates that the higher the TOF calculated, the faster the catalytic rate and the higher the catalytic efficiency. The bimetallic catalyst (Mo2(CO)10) with the highest value of the calculated TOF (2.60 × 10−15 s−1), which is higher than that of Fe2(CO)9 (8.96 × 10−20 s−1) (see Kuriakose et al. in Inorg Chem 51: 377, 2012). The later prove the WGSR catalyst with high performance. Our conclusions will be useful for the design of improved WGSR catalysts in the future.

The effect of heavy tars (toluene and naphthalene) on the electrochemical performance of an anode-supported SOFC running on bio-syngas

The effect of heavy tar compounds on the performance of a Ni-YSZ anode supported solid oxide fuel cell was investigated. Both toluene and naphthalene were chosen as model compounds and tested separately with a simulated bio-syngas. Notably, the effect of naphthalene is almost negligible with pure H2 feed to the SOFC, whereas a severe degradation is observed when using a bio-syngas with an H2:CO = 1. The tar compound showed to have a remarkable effect on the inhibition of the WGS shift-reaction, possibly also on the CO direct electro-oxidation at the three-phase-boundary. An interaction through adsorption of naphthalene on nickel catalytic and electrocatalytic active sites is a plausible explanation for observed degradation and strong performance loss. Different sites seem to be involved for H2 and CO electro-oxidation and also with regard to catalytic water gas shift reaction. Finally, heavy tars (C ≥ 10) must be regarded as a poison more than a fuel for SOFC applications, contrarily to lighter compounds such benzene or toluene that can directly reformed within the anode electrode. The presence of naphthalene strongly increases the risk of anode re-oxidation in a syngas stream as CO conversion to H2 is inhibited and also CH4 conversion is blocked.

Apparent kinetics of the catalyzed water–gas shift reaction in synthetic wood gas

The catalysis of the water–gas shift reaction employing two commercially available catalysts was investigated. The applied feed was a synthetic gas mixture simulating the wood gas derived from the dual fluidized bed steam gasification of biomass. A Co/Mo- and an Fe/Cr-based catalyst were compared in a differentially operated plug flow reactor. The influence of the partial pressures of all reaction partners as well as the effect of temperature were studied, allowing the formation of two power law rate models.(1)r(Co/Mo)=0.044exp-66RTpCO1.28pH2O0.03pCO2-0.11pH2-0.351-1KpCO2pH2pCOpH2O(2)r(Fe/Cr)=300exp-102RTpCO1.37pH2O0.23pCO2-0.16pH2-0.111-1KpCO2pH2pCOpH2OThe CO conversion rates over both catalysts were strongly dependent on the sulfur load in the feed. The presented models were established at a constant H2S concentration of 100vol.ppmdb. At this sulfur load the Fe/Cr-based catalyst should be preferred to the Co/Mo-based catalyst. The partial pressure of H2S could not be included in the power law models because of its influence on the other coefficients of the model.

A new CO conversion quench reactor design

Syntheses downstream of coal gasifiers face specific requirements regarding syngas quality. High syngas H2/CO ratios are a typical requirement. A new quench concept for entrained-flow gasifiers has been developed in order to increase the H2/CO ratio within the quench vessel and thereby minimize efforts in the subsequent catalytic water–gas shift reaction (WGSR). To achieve this target, steam instead of water will be injected into the quench chamber to realize CO conversion via homogeneous WGSR. The concept allows a flexible mode of operation, such as full or partial water quenching with subsequent waste heat utilization for high and medium-pressure steam production. This allows self-sufficiency in terms of steam and additionally offers the potential to increase the overall plant efficiency. To test the concept, three different syngases from various feedstock and two inlet design configurations will be investigated using CFD and compared to one other. The numerical setup has been validated against gasification reactor measurements and simulation, respectively. A sensitivity analysis shows the performance and flexibility of the proposed concept.

From Internal Olefins to Linear Amines: Ruthenium-Catalyzed Domino Water–Gas Shift/Hydroaminomethylation Sequence

A selective ruthenium-catalyzed water–gas shift/hydroformylation of internal olefins and olefin mixtures is reported. This novel domino reaction takes place through a catalytic water–gas shift reaction, subsequent olefin isomerization, followed by hydroformylation and reductive amination. Key to the success for the efficient one-pot process is the use of a specific 2-phosphino-substituted imidazole ligand and triruthenium dodecacarbonyl as precatalyst. Industrially important internal olefins react with various amines to give the corresponding tertiary amines generally in good yield and selectivity. This reaction sequence constitutes an economically attractive and environmentally favorable process for the synthesis of linear amines.

Mechanisms of the water–gas shift reaction catalyzed by carbonyl complexes M(CO)6 (M = Mo, W)

The reduction of water by CO to form CO2 and H2 (Water–Gas Shift Reaction (WGSR)) is an important process catalyzed in homogeneous phase by metal carbonyls. Here we report a theoretical study on four mechanisms of the gas-phase mononuclear carbonyl complexes M(CO)6 (M = Mo, W) catalyzed WGSR. The energetic span model (ESM) proposed by Shaik et al. has been applied to reveal the kinetic behavior of the four catalytic cycles. Our calculation results indicate that W(CO)6 is a promising candidate for an improved WGSR catalyst. An accessible reaction mechanism for the binuclear species M2(CO)10 is also proposed. Mechanistic studies on the formation of and elimination from M2(CO)9COOH− suggest a stepwise process with addition of water to the binuclear hydride species as the key step prompting elimination. Both bimetallic catalysts W2(CO)10 and Mo2(CO)10 show higher activity than mononuclear metal-based catalysts with W2(CO)10 considering as the most efficient catalyst for WGSR. To confirm whether the activity trends in WGSR can be understood in terms of the Hammer–Nørskov d-band model in combination with the linear energy relations, we studied correlations between the turnover frequency (TOF) and the position of the d-band center (εd) relative to the Fermi energy (EF) of various metal complex catalyst. The results indicate that the εd − EF value is useful as a qualitative activity descriptor in catalysis of WGSR. The conclusions will be useful to design of the WGSR catalyst with high performance.

Effect of water density on heterogeneous catalytic water gas shift reaction in the presence of Ru/C, Pd/LaCoO3 and Fe3O4 in supercritical water

Water gas shift reaction in the presence of heterogeneous catalysts such as Ru/C, Pd/LaCoO3 and Fe3O4 was examined in supercritical water at 673K from 0.1 to 0.5g/cm3 of water densities. These catalysts catalyzed water gas shift reaction and the main products were CO2 and H2. CH4 was formed from CO and H2 produced by water gas shift reaction in the presence of Ru/C. CO conversion tended to decrease with increasing water density for all catalysts, which means that water essentially suppressed heterogeneous catalytic water gas shift reaction in supercritical water. The kinetics of water gas shift reaction was analyzed with an elementary-like reaction model using fugacity. The model calculation represented the trend of experimental results and revealed that the suppression of water gas shift reaction in high water density region was probably because water would cover on active sites and stabilize the adsorbed species on catalyst to decrease the ratio of vacancy of active sites on catalyst.

H2 production via water gas shift in a composite Pd membrane reactor prepared by the pore-plating method

In this work, H2 production via catalytic water gas shift reaction in a composite Pd membrane reactor prepared by the ELP “pore-plating” method has been carried out. A completely dense membrane with a Pd thickness of about 10.2 μm over oxidized porous stainless steel support has been prepared. Firstly, permeation measurements with pure gases (H2 and N2) and mixtures (H2 with N2, CO or CO2) at four different temperatures (ranging from 350 to 450 °C) and trans-membrane pressure differences up to 2.5 bar have been carried out. The hydrogen permeance when feeding pure hydrogen is within the range 2.68–3.96·10−4 mol m−2 s−1 Pa−0.5, while it decreases until 0.66–1.35·10−4 mol m−2 s−1 Pa−0.5 for gas mixtures. Furthermore, the membrane has been also tested in a WGS membrane reactor packed with a commercial oxide Fe–Cr catalyst by using a typical methane reformer outlet (dry basis: 70%H2–18%CO–12%CO2) and a stoichiometric H2O/CO ratio. The performance of the reactor was evaluated in terms of CO conversion at different temperatures (ranging from 350 °C to 400 °C) and trans-membrane pressures (from 2.0 to 3.0 bar), at fixed gas hourly space velocity (GHSV) of 5000 h−1. At these conditions, the membrane maintained its integrity and the membrane reactor was able to achieve up to the 59% of CO conversion as compared with 32% of CO conversion reached with conventional packed-bed reactor at the same operating conditions.

Searching for the thermodynamic limit – a DFT study of the step-wise water oxidation of the bipyramidal Cu7cluster

Oxidative degradation of copper in aqueous environments is a major concern in areas such as catalysis, electronics and construction engineering. A particular challenge is to systematically investigate the details of this process for non-ideal copper surfaces and particles under the conditions found in most real applications. To this end, we have used hybrid density functional theory to study the oxidation of a Cu7 cluster in water solution. Especially, the role of a large water coverage is explored. This has resulted in the conclusion that, under atmospheric H2 pressures, the thermodynamically most favored state of degradation is achieved upon the generation of four H2 molecules (i.e. Cu7 + 8H2O → Cu7(OH)8 + 4H2) in both condensed and gas phases. This state corresponds to an average oxidation state below Cu(I). The calculations suggest that the oxidation reaction is slow at ambient temperatures with the water dissociation as the rate-limiting step. Our findings are expected to have implication for, among other areas, the copper catalyzed water-gas shift reaction, and for the general understanding of copper corrosion in aqueous environments.

Theoretical Investigation of Water Gas Shift Reaction Catalyzed by Iron Group Carbonyl Complexes M(CO)5 (M = Fe, Ru, Os)

We have investigated the mechanism of M(CO)(5) (M = Fe, Ru, Os) catalyzed water gas shift reaction (WGSR) by using density functional theory and ab initio calculations. Our calculation results indicate that the whole reaction cycle consists of six steps: 1 → 2 → 3 → 4 → 5 → 6 → 2. In this stepwise mechanism the metals Fe, Ru, and Os behave generally in a similar way. However, crucial differences appear in steps 3 → 4 → 5 which involve dihydride M(H)(2)(CO)(3)COOH(-) (4') and/or dihydrogen complex MH(2)(CO)(3)COOH(-) (4). The stability of the dihydrogen complexes becomes weaker down the iron group. The dihydrogen complex 4_Fe is only 11.1 kJ/mol less stable than its dihydride 4'_Fe at the B3LYP/II(f)++//B3LYP/II(f) level. Due to very low energy barrier it is very easy to realize the transform from 4_Fe to 4'_Fe and vice versa, and thus for Fe there is no substantial difference to differentiate 4 and 4' for the reaction cycle. The most possible key intermediate 4'_Ru is 38.2 kJ/mol more stable than 4_Ru. However, the barrier for the conversion 3_Ru → 4'_Ru is 23.8 kJ/mol higher than that for 3_Ru → 4_Ru. Additionally, 4'_Ru has to go through 4_Ru to complete dehydrogenation 4'_Ru → 5_Ru. The concerted mechanism 4'_Ru → 6_Ru, in which the CO group attacks ruthenium while H(2) dissociates, can be excluded. In contrast to Fe and Ru, the dihydrogen complex of Os is too unstable to exist at the level of theory. Moreover, we predict Fe and Ru species are more favorable than Os species for the WGSR, because the energy barriers for the 4 → 5 processes of Fe and Ru are only 38.9 and 16.2 kJ/mol, respectively, whereas 140.5 kJ/mol is calculated for the conversion 4' → 5 of Os, which is significantly higher. In general, the calculations are in good agreement with available experimental data. We hope that our work will be beneficial to the development and design of the WGSR catalyst with high performance.